I am an Electronics Engineer with a Master in Optics. After graduating, I worked in an Optics Research Center in Mexico (CIO) for 8 years as part of the Technology division, working in projects for the industry and supporting IR technology research. Currently, I am working at the Wellman Center for Photomedicine in the Massachusetts General Hospital as a Research Engineer. Here I develop prototypes, computational tools and optical/electronic devices that help fellows take measurements or complete their work more efficiently. I also do some research on my own on the field of UV fluorescence of tissue and tissue oximetry.I count MATLAB and Labview programming among my skills, as well as knowledge of spectroscopy, infrared and signal processing.Other of my interests are genetics, phylogeny and big data.

Publications (17)

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Background and Objectives: UV Fluorescence Excitation Imaging (u-FEI) has been shown to be a simple but robust, non-invasive and non-contact method to visualize cells with a high proliferative rate. We had demonstrated the ability of u-FEI to visualize the re-epithelialization of skin wounds in an organ culture system. In this work, we investigated the potential of u-FEI for visualization of wound closure of partial and full-thickness skin wounds.
Study Design: Partial and full-thickness skin wounds were created in the tail of rats. Wounds were imaged weekly using u-FEI system operating at 295/340nm excitation/emission wavelengths, which correspond to the excitation/emission bands of the endogenous fluorophore tryptophan. Histology and immunohistology were used to determine the association between fluorescence intensity and proliferation of keratinocyte cells.
Results: Similar to human skin, the skin of a rat tail heals by re-epithelialization. Keratinocytes migrated and proliferated from the edge and skin appendages of partial-skin wounds to close the wound by creating neo-epidermis. The fluorescence intensity of the whole wound area increased uniformly during week one and decreased to non-wounded control levels around week three. For full-thickness wounds, keratinocytes migrated only from the wound edges as skin appendages were missing. The fluorescence intensity was higher by the wound edge and marched towards the center during healing. H&E and immunohistology show that changes in fluorescence intensity corresponded to newly formed epidermis.
Conclusions: u-FEI of tryptophan allowed visualization of wound closure of partial and full-thickness skin wounds in an in vivo model of wound healing by epithelialization.

Marine mammals possess impressive breath-holding capabilities made possible by physiological adjustments during dives. Studying marine mammals in their natural environment unravels vital information about these physiological adjustments particularly when we can monitor altered dive behavior in response to stressful situations such as human-induced oceanic disturbances, presence of predators and altered prey distributions. An important indicator of physiological status during submergence is the change in oxygen saturation in the muscles and blood of these mammals. In this work, we aim to investigate oxygen storage and consumption in the muscles of free-diving elephant seals when exposed to disturbances such as sonar or predator sounds while they are at sea. Optical oxygen sensors are a mature technology with multiple medical applications that provide a way to measure oxygenation changes in biological tissues in a minimally invasive manner. While these sensors are well calibrated and readily available for humans, they are still inadequate for marine mammals primarily due to a very small number of test candidates and therefore little data is available for validation and calibration. We propose a probe geometry and associated mathematical model for measuring muscle oxygenation in seals based on near infrared diffuse transport with no need for calibration. A prototype based on this concept has been designed and tested on humans and rats. We use the test results to discuss the advantages and limitations of the approach. We also detail the constraints on size, sensor location, electronics, light source properties and detector characteristics posed by the unique biology of seals.

Keratoconus is an eye disease in which the cornea progressively deforms due to loss of cornea mechanical rigidity, and thus causes deterioration of visual acuity. Techniques to characterize the mechanical characteristics of the cornea are important to better monitor changes and response to treatments. To investigate the feasibility of using the endogenous fluorescence of cornea for monitoring alterations of its mechanical rigidity, linear tensiometry was used to quantitate stiffness and Young’s modulus (YM) after treatments that increase cornea stiffness (collagen photocross-linking) or decrease stiffness (enzymatic digestion). The endogenous ultraviolet fluorescence of cornea was also measured before and after these treatments. The fluorescence excitation/emission spectral ranges were 280 to 430/390 to 520 nm, respectively. A correlation analysis was carried out to identify fluorescence excitation/emission pairs whose intensity changes correlated with the stiffness. A positive correlation was found between variations in fluorescence intensity of the 415-/485-nm excitation/emission pair and YM of photocross-linked corneas. After treatment of corneas with pepsin, the YM decreased as the fluorescence intensity at 290-/390-nm wavelengths decreased. For weakening of corneas with collagenase, only qualitative changes in the fluorescence spectrum were observed. Changes in the concentration of native or newly created fluorescent molecular species contain information that may be directly or indirectly related to the mechanical structure of the cornea.

Intrinsic UV fluorescence imaging is a technique that permits the observation of spatial differences in emitted fluorescence. It relies on the fluorescence produced by the innate fluorophores in the sample, and thus can be used for marker-less in-vivo assessment of tissue. It has been studied as a tool for the study of the skin, specifically for the classification of lesions, the delimitation of lesion borders and the study of wound healing, among others. In its most basic setup, a sample is excited with a narrow-band UV light source and the resulting fluorescence is imaged with a UV sensitive camera filtered to the emission wavelength of interest. By carefully selecting the excitation/emission pair, we can observe changes in fluorescence associated with physiological processes. One of the main drawbacks of this simple setup is the inability to observe more than a single excitation/emission pair at the same time, as some phenomena are better studied when two or more different pairs are studied simultaneously. In this work, we describe the design and the hardware and software implementation of a dual wavelength portable UV fluorescence imaging system. Its main components are an UV camera, a dual wavelength UV LED illuminator (295 and 345 nm) and two different emission filters (345 and 390 nm) that can be swapped by a mechanical filter wheel. The system is operated using a laptop computer and custom software that performs basic pre-processing to improve the image. The system was designed to allow us to image fluorescent peaks of tryptophan and collagen cross links in order to study wound healing progression.

Background and Objectives: Keratoconus is a disease characterized by progressive steepening and thinning of the cornea, altering visual acuity and sometimes potentiating the need for corneal transplant if the disease progresses.1–3 Corneal crosslinking, a procedure that uses topical riboflavin and UV light to increase the stiffness of the cornea through the creation of collagen crosslinks was recently approved by the FDA for use in the U.S. The objective of the present study was to investigate whether endogenous collagen fluorescence changes following treatment can be correlated to alterations in the stiffness of the cornea, thereby guiding treatment parameters. Study Design and Results: 78 ex-vivo rabbit eyes divided into three groups: riboflavin solution plus UV irradiation, dextran solution plus UV irradiation, and riboflavin solution only. An additional group of eyes received no treatment. The epithelium was removed from each sample and topical riboflavin was applied. Eyes were irradiated with a 365 nm black ray UV lamp for various treatment times, ranging from half the clinical treatment time to three times the length. Mechanical testing was performed to determine the force/displacement relationship for the various treatment times. Fluorescence spectral changes following treatment corresponded with changes in stiffness. In particular, a decrease in the value of fluorescence intensity at 290/340 nm excitation/emission wavelengths corresponded to an increase in corneal stiffness following treatment. It may be possible to use fluorescence spectral changes of endogenous corneal crosslinks to evaluate mechanical stiffness changes non-invasively.

Non-subjective, minimally-invasive, and quantifying techniques may support development and evaluation of a fibrosis regression treatment. The build-up of extracellular matrix in liver fibrosis may result on changes of the endogenous fluorescence of tissue. In this work, we evaluate the fluorescence excitation/emission matrix in the UV range for several bulk samples of murine hepatic tissue preserved in different media. Chemical changes on tissue, caused by formaldehyde preservation, alter the endogenous fluorescence spectra. To avoid these drawbacks, phosphate-buffered saline (PBS) or Iscove’s Modified Dulbecco’s Medium were used. PBS buffer showed to be the less harmful and cost-effective preservation medium to study the endogenous fluorescence in fibrotic tissue.

Background and Objectives: We have previously demonstrated the efficacy of a non-invasive, non-contact, fast and
simple but robust fluorescence imaging (u-FEI) method to monitor the healing of skin wounds in vitro. This system can
image highly-proliferating cellular processes (295/340 nm excitation/emission wavelengths) to study epithelialization in
a cultured wound model. The objective of the current work is to evaluate the suitability of u-FEI for monitoring wound
re-epithelialization in vivo.
Study Design: Full-thickness wounds were created in the tail of rats and imaged weekly using u-FEI at 295/340nm
excitation/emission wavelengths. Histology was used to investigate the correlation between the spatial distribution and
intensity of fluorescence and the extent of wound epithelialization. In addition, the expression of the nuclear protein
Ki67 was used to confirm the association between the proliferation of keratinocyte cells and the intensity of
fluorescence.
Results: Keratinocytes forming neo-epidermis exhibited higher fluorescence intensity than the keratinocytes not
involved in re-epithelialization. In full-thickness wounds the fluorescence first appeared at the wound edge where
keratinocytes initiated the epithelialization process. Fluorescence intensity increased towards the center as the
keratinocytes partially covered the wound. As the wound healed, fluorescence decreased at the edges and was present
only at the center as the keratinocytes completely covered the wound at day 21. Histology demonstrated that changes in
fluorescence intensity from the 295/340nm band corresponded to newly formed epidermis.
Conclusions: u-FEI at 295/340nm allows visualization of proliferating keratinocyte cells during re-epithelialization of
wounds in vivo, potentially providing a quantitative, objective and simple method for evaluating wound closure in the
clinic.

The skin contains several fluorescent molecules or fluorophores that serve as markers of structure, function and composition. UV fluorescence excitation photography is a simple and effective way to image specific intrinsic fluorophores, such as the one ascribed to tryptophan which emits at a wavelength of 345 nm upon excitation at 295 nm, and is a marker of cellular proliferation. Earlier, we built a clinical UV photography system to image cellular proliferation. In some samples, the naturally low intensity of the fluorescence can make it difficult to separate the fluorescence of cells in higher proliferation states from background fluorescence and other imaging artifacts -- like electronic noise. In this work, we describe a statistical image segmentation method to separate the fluorescence of interest. Statistical image segmentation is based on image averaging, background subtraction and pixel statistics. This method allows to better quantify the intensity and surface distributions of fluorescence, which in turn simplify the detection of borders. Using this method we delineated the borders of highly-proliferative skin conditions and diseases, in particular, allergic contact dermatitis, psoriatic lesions and basal cell carcinoma. Segmented images clearly define lesion borders. UV fluorescence excitation photography along with statistical image segmentation may serve as a quick and simple diagnostic tool for clinicians.

The stiffness or rigidity of the extracellular matrix (ECM) regulates cell response. Established mechanical tests to measure stiffness, such as indentation and tensile tests, are invasive and destructive to the sample. Endogenous or native molecules to cells and ECM components, like tryptophan and cross-links of collagen, display fluorescence upon irradiation with ultraviolet light. Most likely, the concentration of these endogenous fluorophores changes as the stiffness of the ECM changes. In this work we investigate the endogenous fluorescence of collagen gels containing fibroblasts as a non-invasive non-destructive method to measure stiffness of the ECM. Human fibroblast cells were cultured in three-dimensional gels of type I collagen (50,000 cells/ml). This construct is a simple model of tissue contraction. During contraction, changes in the excitation-emission matrix (a fluorescence map in the 240-520/290-530 nm range) of constructs were measured with a spectrofluoremeter, and changes in stiffness were measured with a standard indentation test over 16 days. Results show that a progressive increase in fluorescence of the 290/340 nm excitation-emission pair correlates with a progressive increase in stiffness (r=0.9, α=0.5). The fluorescence of this excitation-emission pair is ascribed to tryptophan and variations in the fluorescence of this pair correlate with cellular proliferation. In this tissue model, the endogenous functional fluorescence of proliferating fibroblast cells is a biomechanical marker of stiffness of the ECM.

Degradation and destruction of articular cartilage is the etiology of osteoarthritis (OA), an entity second only to cardiovascular disease as a cause of disability in the United States. Joint mechanics and cartilage biochemistry are believed to play a role in OA; an optical tool to detect structural and chemical changes in articular cartilage might offer benefit for its early detection and treatment. The objective of the present study was to identify the spectral changes in intrinsic ultraviolet (UV) fluorescence of cartilage that occur after proteolytic digestion of cartilage. Bovine articular cartilage samples were incubated in varying concentrations of collagenase ranging from 10ug/mL up to 5mg/mL for 18 hours at 37°C, a model of OA. Pre- and post-incubation measurements were taken of the UV excitation-emission spectrum of each cartilage sample. Mechanical tests were performed to determine the pre- and post-digestion force/displacement ratio associated with indentation of each sample. Spectral changes in intrinsic cartilage fluorescence and stiffness of the cartilage were associated with proteolytic digestion. In particular, changes in the relative intensity of fluorescence peaks associated with pentosidine crosslinks (330 nm excitation, 390 nm emission) and tryptophan (290 nm excitation, 340 nm emission) were found to correlate with different degrees of cartilage digestion and cartilage stiffness. In principle, it may be possible to use UV fluorescence spectral data for early detection of damage to articular cartilage, and as a surrogate measure for cartilage stiffness.

Wound size is a key parameter in monitoring healing. Current methods to measure wound size are often subjective, time-consuming
and marginally invasive. Recently, we developed a non-invasive, non-contact, fast and simple but robust
fluorescence imaging (u-FEI) method to monitor the healing of skin wounds. This method exploits the fluorescence of
native molecules to tissue as functional and structural markers. The objective of the present study is to demonstrate the
feasibility of using variations in the fluorescence intensity of tryptophan and cross-links of collagen to evaluate
proliferation of keratinocyte cells and quantitate size of wound during healing, respectively. Circular dermal wounds
were created in ex vivo human skin and cultured in different media. Two serial fluorescence images of tryptophan and
collagen cross-links were acquired every two days. Histology and immunohistology were used to validate correlation
between fluorescence and epithelialization. Images of collagen cross-links show fluorescence of the exposed dermis and,
hence, are a measure of wound area. Images of tryptophan show higher fluorescence intensity of proliferating
keratinocytes forming new epithelium, as compared to surrounding keratinocytes not involved in epithelialization. These
images are complementary since collagen cross-links report on structure while tryptophan reports on function. HE and
immunohistology show that tryptophan fluorescence correlates with newly formed epidermis. We have established a
fluorescence imaging method for studying epithelialization processes during wound healing in a skin organ culture
model, our approach has the potential to provide a non-invasive, non-contact, quick, objective and direct method for
quantitative measurements in wound healing in vivo.

Collagen is a long fibrous structural protein that imparts mechanical support, strength and elasticity to many tissues. The state of the tissue mechanical environment is related to tissue physiology, disease and function. In the cornea, the collagen network is responsible for its shape and clarity; disruption of this network results in degradation of visual acuity, for example in the keratoconus eye disease. The objective of the present study is to investigate the feasibility of using the endogenous fluorescence of collagen crosslinks to evaluate variations in the mechanical state of tissue, in particular, the stiffness of cornea in response to different degrees of photo-crosslinking or RGX treatment—a novel keratoconus treatment. After removing the epithelium, rabbit corneas were stained with Rose Bengal and then irradiated with a 532 nm solid-state laser. Analysis of the excitation spectra obtained by fluorescence spectroscopy shows a correlation between the fluorescence intensity at 370/460 nm excitation/emission wavelengths and the mechanical properties. In principle, it may be feasible to use the endogenous fluorescence of collagen crosslinks to evaluate the mechanical stiffness of cornea non-invasively and in situ.

In this work we characterized several state-of-the-art high sensitivity optical detectors. We compared
avalanche photo diode devices (APD) with multi-pixel photon counting devices (MPPC) in several
characteristics such as detection efficiency and response times. We then discussed some of the results.

Mexico possesses a large cultural heritage of paintings, elaborated after the European explorers encountered the New World.
The interest in documenting these treasures was recently renewed, with the development of nondestructive remote
techniques. We examined an undocumented painting for the presence of any invisible signatures, dates, or under-drawings.
We employed several illumination-detection schemes, including IR broadband and LED arrays to achieve this purpose. We
made visible the signature at about 1 μm and the date at 1.2 μm.

We examined old, not-well documented paintings before the process of restoration was started, to look for the presence of any invisible signatures and dates, as well as original line drawings and possible painted-over or hidden images. We connected IR LEDs in two-dimensional arrays to allow us to sample the surface of the artwork with approximately uniform illumination, but at different peak wavelengths. We describe the extended area infrared LED illumination sources as to their geometrical arrangement, and their resulting spectral, spatial, and power output characteristics. With these light sources, we were able to make invisible information available for review and critical assessment by the art historians.

We propose and evaluate an optical "image splitter" by which we can capture two simultaneous infrared images of a
single object, using a single detector. With this device, we can perform experiments in which we are interested to
observe transitory phenomena in two different spectral bands, without losing the spatial information of the test subject.
We also present experimental results of using this array for mid-infrared flame analysis.

We have been working on improving several specific areas to make optical coherence tomography more efficient. First,
we are using simultaneously a number of apertures in order to accelerate scanning over the object surface. Second, to
increase the depth of use of the technique we devised ways of lengthening compensating path in one interferometer arm.
In this work, we describe both of these techniques and their overall contribution to the performance improvements.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews